Identification of Entamoeba histolytica thiol-specific antioxidant as a GalNAc lectin-associated protein.

Entamoeba histolytica is a human intestinal parasite that causes amebic dysentery. A cell surface amebic adhesin, the galactose and N-acetyl-D-galactosamine inhibitable (GalNAc) lectin mediates amebic adherence to and contact-dependent killing of host cells. Previous work has suggested that the GalNAc lectin transduces signals via protein interactions with its short cytoplasmic domain. We used a yeast two-hybrid system to screen an E. histolytica cDNA library for proteins that interact with the GalNAc lectin cytoplasmic domain. One isolate was the E. histolytica thiol-specific antioxidant (TSA). TSA is an enzyme that detoxifies hydrogen peroxide. TSA did not interact in yeast two-hybrid experiments with a mutant version of the lectin cytoplasmic domain, confirming the specificity of the lectin-TSA interaction. Furthermore, mutational analyses of the TSA isolate demonstrated that an in-frame five amino acid sequence introduced between amino acids 61-62 yielded a TSA mutant that did not interact with the lectin cytoplasmic domain upon expression in the yeast two-hybrid system. The association of TSA and GalNAc lectin was further supported by co-immunoaffinity purification. Confocal microscopy demonstrated co-localization of TSA and GalNAc lectin at sites of ameba:host cell contact. Recruitment of TSA by the GalNAc lectin suggests a novel mechanism of parasite defense against reactive oxygen intermediates generated by host peripheral mononuclear cells.